Gravity: Analog TDS Sensor for Arduino | Total Dissolved Solids Meter | Water Quality Sensor Compatible with Arduino: Amazon.com: Industrial & Scientific
Inexpensive DIY conductivity sensor – EnviroDIY
DIY Soil EC/Salinity Meter || Measure Soil Conductivity & Salinity using Arduino & Soil EC Sensor - YouTube
DIY Soil EC Salinity Meter using Arduino & Soil EC Sensor
DIY Soil EC Salinity Meter using Arduino & Soil EC Sensor